THE DEEP VEINS OF THE UPPER EXTREMITY 739 



lower border of the cartilage of the first rib close to the sternum on the right 

 side, and, descending vertically, enters the pericardium about an inch and a half 

 above the heart, and terminates in the upper part of the right auricle opposite 

 the upper border of the third right costal cartilage. In its course it describes a 

 slight curve, the convexity of which is to the right side. 



Relations. In front, with the pericardium and process of cervical fascia which is con- 

 tinuous with it; these separate it from the thymus gland, the sternum, and the second and third 

 right costal cartilages; behind, with the root of the right lung. On its right s-ide, it is in relation 

 with the phrenic nerve and right pleura; on its left side, with the commencement of the innom- 

 inate arterv and ascending part of the aorta, the latter somewhat overlapping it. The portion 

 contained within the pericardium is covered in front and laterally by the serous layer of that 

 membrane. It receives the vena azygos major just before it enters the pericardium, and several 

 small veins from the pericardium and parts in the mediastinum. The superior vena cava has no 

 valves. 



The azygos veins are three in number; they collect the blood from the majority 

 of the intercostal spaces, and connect the superior and inferior venae cavee. 



The vena azygos major (v. azygos) (Fig. 515) commences opposite the first or 

 second lumbar vertebra by a branch from the right lumbar veins, called the right 

 ascending lumbar vein (v. lumbalis ascendens dextra); sometimes by a branch from 

 the right renal vein or from the inferior vena cava. It enters the thorax through 

 the aortic opening in the Diaphragm, and passes along the right side of the ver- 

 tebral column to the fourth thoracic vertebra, where it arches forward over the 

 root of the right lung, and terminates in the superior vena cava just before that 

 vessel enters the pericardium. While passing through the aortic opening of the 

 Diaphragm it lies with the thoracic duct on the right side of the aorta, and in the 

 thorax it lies upon the intercostal arteries on the right side of the aorta and thoracic 

 duct, and is partly covered by pleura. 



Tributaries. It receives the lower ten posterior intercostal veins of the right side, 

 the upper two or three of these opening, first of all, into the right superior inter- 

 costal vein. It receives the azygos minor veins, several oesophageal, mediastinal 

 and pericardial veins; near its termination, the right bronchial vein; and generally 

 the right superior intercostal vein. A few imperfect valves are found in this vein; 

 but its tributaries are provided with complete valves. \ 



The intercostal veins (vv. intercostales) are divided into anterior and posterior 

 intercostals. 



The anterior intercostal veins are tributaries of the internal mammary or the 

 musculophrenic veins (p. 737). 



The posterior intercostal veins (Fig. 515) number eleven on each side, there 

 being one vein in each intercostal space. Each vein lies in the groove at the 

 i lower margin of the rib above the corresponding intercostal artery. On the right 

 (side the first posterior intercostal vein crosses the neck of the first rib anteriorly 

 'and opens into the vertebral vein or the innominate vein. The first posterior 

 jintercostal of the left side follows a like course, and empties into the vertebral 

 or innominate vein. The posterior intercostals of the right side, from the fifth 

 jto the eleventh, inclusive, open individually into the vena azygos major. The 

 left upper azygos vein is formed by the fifth, sixth, seventh, and eighth posterior 

 intercostals of the left side. The left lower azygos vein receives the ninth, tenth, 

 and eleventh left posterior intercostals. 



The vena agygos minor inferior (v. hemiazygos] (Fig. 515) commences in the 



lumbar region by a branch from one of the lumbar veins, ascending lumbar (v. 



lumbalis ascendens}, or from the left renal. It enters the thorax through the left 



Dems of the Diaphragm, and, ascending on the left side of the vertebral column 



IBS high as the ninth thoracic vertebra, passes across the vertebral column, behind 



line aorta, o?sophagus, and thoracic duct, to terminate in the major azygos vein. 



